As an update, I realized that the problem did not actually happen while I was
pressing two keys (N+Left) but three (Up+N+Left) since the Up key has to be
pressed most of the time. Sorry for this overlook.
The xev output when pressing the Up+N+Left combination shows that the Left
keypress does not register:
KeyPress event, serial 35, synthetic NO, window 0x4e00001,
root 0xfd, subw 0x0, time 5040846, (762,-66), root:(766,58),
state 0x10, keycode 111 (keysym 0xff52, Up), same_screen YES,
XLookupString gives 0 bytes:
XmbLookupString gives 0 bytes:
XFilterEvent returns: False
KeyPress event, serial 38, synthetic NO, window 0x4e00001,
root 0xfd, subw 0x0, time 5041078, (762,-66), root:(766,58),
state 0x10, keycode 57 (keysym 0x6e, n), same_screen YES,
XLookupString gives 1 bytes: (6e) "n"
XmbLookupString gives 1 bytes: (6e) "n"
XFilterEvent returns: False
KeyRelease event, serial 38, synthetic NO, window 0x4e00001,
root 0xfd, subw 0x0, time 5041455, (762,-66), root:(766,58),
state 0x10, keycode 57 (keysym 0x6e, n), same_screen YES,
XLookupString gives 1 bytes: (6e) "n"
XFilterEvent returns: False
KeyRelease event, serial 38, synthetic NO, window 0x4e00001,
root 0xfd, subw 0x0, time 5041637, (762,-66), root:(766,58),
state 0x10, keycode 111 (keysym 0xff52, Up), same_screen YES,
XLookupString gives 0 bytes:
XFilterEvent returns: False
With this in mind, I kept searching until I found that entry on the STK FAQ,
under "Gameplay quesions" (and not under "Technical questions" where I had
initially been looking for an answer) :
"Why don't some keyboard keys work when pressed simultaneously?
When playing with a keyboard, you may experience issues when pressing
multiple keys simultaneously, for instance trying to use nitro while
accelerating and turning. In such situations, some keypress may not register.
This is however not a bug of SuperTuxKart, but a phyiscal limitation of your
keyboard, most keyboards can only handle so many keys pressed at the same
time (for more detailed information, please check
http://www.sjbaker.org/wiki/index.php?title=Keyboards_Are_Evil). The solution
is to use a gaming input device (gamepad, or gaming keyboard), or tweak the
keys configuration to find keys that your keyboard will be able to register
simultaneously."
I would add that using a different keyboard might also help, as I had been
doing for a while for other reasons and as suggested above.
Thank you both for your helpful hints. I might add something in the hardware
section in the doc here in case other users encounter similar keystroke
conflicts.
